This disclosure relates to polymer compositions, methods to synthesize the polymer compositions and articles made from the compositions.
Many polymer-based articles are manufactured by injection or other molding processes. In order to obtain good mechanical properties such as high modulus, different approaches have been tried, such as use of filler to reinforce the polymers. Different types of fillers such as glass fibers, aramid fibers, carbon fibers, and various particulate fillers have been used. However, addition of these fillers often leads to brittle failure of the polymer and can lower the impact strength of the resin. Where improved ductility has been obtained, such as in the case of aramid fillers, the modulus obtained is very low. In addition, use of fillers can present processing difficulties, due at least in part to lack of compatibility of the filler with the polymer matrix. Such incompatibility can also result in molding and flow-related problems.
Despite advances in the art and the success of many filled polymer compositions, there remains a continuing need for improved combinations of properties such as higher modulus, improved ductility, improved impact, and/or improved melt flow characteristics, so that molding operations can be performed more rapidly and with improved economics. Also it is desirable that the article has good impact resistance and ductility without the consequent loss of other desirable characteristics. Typically, it is difficult to obtain high modulus, good flow, and good ductility and impact strength in a particular polymer composition.
Polytetrafluoroethylene (PTFE) fibers have been used as fillers in polymer compositions, but can aggregate in the matrix resin, making it very difficult to obtain a uniform composition. Polytetrafluoroethylene and other fluoropolymers have also been used as additives in thermoplastic polymers in order to improve certain properties of the polymers. The use of relatively small amounts, for example about 0.1 to about 1 percent by weight, of fluoropolymers as an anti-drip additive in flame retardant grades of thermoplastic resin molding compositions is described, for example, in U.S. Pat. Nos. 4,810,739, 4,579,906, and 4,810,739. The use of sintered PTFE in highly filled thermoplastic compositions as low friction additives is disclosed in U.S. Pat. No. 5,879,791. A drawback to the use of fluoropolymer additives exists, however, in that such additives have poor dispersibility in many polymers.
U.S. Pat. No. 5,804,654 teaches a process for production of encapsulated fluoropolymer, wherein the encapsulant is any polymer or copolymer obtainable by emulsion polymerization. The encapsulated fluoropolymers are used in a number of polymer compositions, particularly for providing flame retardance to the composition. U.S. Pat. No. 5,962,587 and U.S. Pat. No. 6,025,441 describes thermoplastic polymer compositions comprising encapsulated PTFE where improved mechanical properties were observed. However, the prior art does not appear to recognize or suggest particular combinations or processing for PTFE-containing compositions that provide an optimum balance of mechanical properties. Therefore, there is a continuing in the art for compositions, methods, and articles that can provide a balanced mechanical property profile, particularly improved tensile modulus.